Study of optical output couplers for submillimeter wavelength backward-wave oscillators (BWO's)

The machining of slow wave structures for high frequency BWO's is extremely difficult beyond l THz. Recently a microfabrication technique using photolithography and ion-beam assisted etching has been used to construct a prototype BWO operating at 200 to 265 GHz. The output coupler for such tubes remains a problem. Waveguides do not exist or are very lossy at the frequencies of interest (300 to 2000 GHz). This paper discusses several scaled experiments of optical output couplers for submillimeter BWO's. Various designs of planar antennas (Vivaldi horns) and lens-feed systems (hyperhemispherical lens) were constructed and tested between 20 and 100 GHz using a spectrum analyzer. The lens system was also tested at 337 GHz using a CO₂ pumped FIR laser.     

Direct SNAr amination of fluorinated imidazo[4,5-c]pyridine nucleosides: efficient syntheses of 3-fluoro-3-deazaadenosine analogs

This paper describes the ready preparation of 3,6-difluoro-3-deazapurine (4,7-difluoroimidazo[4,5-c]pyridine). This novel base was glycosylated under mild conditions using three different ribose sugar analogs. 3,6-Difluoro-3-deazapurine ribonucleoside analogs underwent direct S_NAr amination reactions with liquid ammonia to give 3-fluoro-3-deazaadenosine analogs in excellent yield; in contrast, 6-chloro-3-fluoro-3-deazapurine nucleosides were inert under similar reaction conditions.     

Sensitivity theorems in integer linear programming

We consider integer linear programming problems with a fixed coefficient matrix and varying objective function and right-hand-side vector. Among our results, we show that, for any optimal solution to a linear program max{wx: Axb}, the distance to the nearest optimal solution to the corresponding integer program is at most the dimension of the problem multiplied by the largest subdeterminant of the integral matrixA. Using this, we strengthen several integer programming proximity results of Blair and Jeroslow; Graver; and Wolsey. We also show that the Chvátal rank of a polyhedron {x: Axb} can be bounded above by a function of the matrixA, independent of the vectorb, a result which, as Blair observed, is equivalent to Blair and Jeroslow's theorem that each integer programming value function is a Gomory function.Supported by a grant from the Alexander von Humboldt Stiftung.Since September 1985: Department of Operations Research, Upson Hall, Cornell University, Ithaca, NY 14853, USA.Partially supported by the Sonderforschungbereich 21 (DFG), Institut für Ökonometrie und Operations Research of the University of Bonn, FR Germany.     

Conversion electron and X-ray Mössbauer studies of the corrosion products and surface modifications in stainless and weathering steels

The study of the corrosion products formed on the surface of Type 316 stainless steel exposed to chlorinated seawater for 18 days shows that ferrihydrite and lepidocrocite are the first oxides to form. The surface also shows the formation of a martensite when it is cleaned by light brushing before exposure.Samples of weathering steel, ASTM A242 Type 1, exposed for 51/2 years to either a marine or inland rural environment have been studied between 100K and 400K using CEMS and XMS. Different amounts of hydroxoxides are present on the surface of each sample. The steel exposed to the inland environment contains more -FeOOH.The author acknowledges the LaQue Center of Corrosion Technology, NC, and the Bethlehem Steel Corporation, PA, for preparing the samples.     

Operational logics and the Hahn-Jordan property

The main result established in this paper is the following: If the base normed spaceV of completely additive weights is a norm-determining subspace of the space of finitely additive weights V acting on the order unit space spanning the operational logic, thenV has the -Jordan-Hahn property iff V has the approximate Jordan-Hahn property. Several examples illustrating the theory are given.Dedicated to the memory of Professor Charles H. Randall.